Hypertension is more prevalent in black than white men, and is more prevalent in men than women. Furthermore, even controlling for blood pressure, concentric left ventricular hypertrophy, an early structural adaptation of hypertension, is more prevalent in black than white men, and more prevalent in men than women. Concentric left ventricular hypertrophy is the strongest predictor, other than age, of the cardiovascular morbidity associated with high blood pressure. The proposed research will investigate the role of biobehavioral factors in the pathogenesis of concentric left ventricular hypertrophy. A biracial sample of two hundred normotensive and borderline hypertensive men and women aged 25-39 years, will be tested. Concentric left ventricular hypertrophy and concentric remodelling will be assessed by echocardiographic measures of left ventricular mass and relative wall thickness. Laboratory procedures will be used to: (i) assess hemodynamic and neurohumoral responses during exposure to a diverse battery of physical and psychological stressors, and; (ii) evaluate alpha and beta adrenergic receptor responsiveness, baroreceptor reflex gain and minimal forearm vascular resistance. Since blood pressure during a typical workday is an established predictor of left ventricular hypertrophy, it will also be assessed. A new biobehavioral model will be tested that implicates the hemodynamic pattern of behaviorally-evoked pressor responses in the pathogenesis of concentric left ventricular hypertrophy. One prediction of this model is that a predisposition to exhibit increased vascular resistance during stress (characteristic of black men) will favor the development of concentric hypertrophy. Thus, systemic vascular resistance responses, evaluated in the laboratory, are hypothesized to independently predict left ventricular mass and relative wall thickness, even after controlling for established risk factors, including workday blood pressure. Sympathetic nervous system function will be examined to test hypothesized mechanisms responsible for race and gender differences in the hemodynamic patterns of blood pressure regulation. The results of these studies should emphasize the impOrtance of race and gender in prescribing pharmacological and/or behavioral treatment for hypertensive heart disease.